Methods in which solid particles are in suspension in a fluid and thereby form a fluidized bed through which this fluid passes are well known. When the fluid is injected tangentially to the side wall of a cylindrical reactor, it can transfer part of its kinetic energy to the solid particles in order to make them rotate, and if the energy transfer is sufficient, this rotational movement produces a centrifugal force which can maintain the solid particles along the wall of the reactor, thereby forming a rotating solid particles, whereof the surface is approximately an inverted truncated cone, if the reactor is vertical. Such a method is the subject of Belgian patent application No. 2004/0186, filed on 14 Apr. 2004, in the name of the same inventor.
To obtain a high concentration of solid particles in a conventional fluidized bed, subject to the force of gravity alone, the fluid passing through the fluidized bed must exert on the solid particles an upward pressure lower than the downward pressure of the solid particles due to the force of gravity, and its upward velocity must therefore be low, thereby limiting the fluid flow rate which can pass through the fluidized bed and the difference in velocity of the fluid to that of the solid particles in suspension in this fluid.
In a rotating fluidized bed, in which the centrifugal force may be substantially higher than the force of gravity, the centripetal pressure exerted by the fluid passing radially through the fluidized bed may be substantially higher and therefore its flow rate and its difference in velocity to that of the solid particles may both be substantially higher, thereby improving the contact between the fluid and the solid particles and substantially increasing the volume of fluid that can pass through the fluidized bed and therefore also its capacity to cool, heat and/or dry the solid particles.
If the rotating fluidized bed is supported by a fixed cylindrical wall along which it must slide, the pressure exerted by the solid particles against this fixed cylindrical wall slows these solid particles down to an extent commensurate with the thickness, density and rotational velocity of the fluidized bed. The rotational velocity will decrease rapidly if the angular momentum of rotation is not maintained using rotating mechanical means, with the problems associated with the presence of moving equipment inside the reactor, and/or by the injection of fluid at high velocity, in the direction of rotation of the fluidized bed.
However, when a fluid jet is injected at high velocity into a large reactor, it is rapidly slowed down by its expansion in the reactor, depending on the conditions under which it is injected, thereby limiting its ability to transfer a significant momentum to the solid particles. This is why, unless other mechanical means are used to rotate the fluidized bed, it is necessary to have a very high fluid flow rate to be able to transfer to the solid particles the momentum necessary to maintain a sufficient rotational velocity to maintain them along the cylindrical wall of the reactor, and if the fluid density is much lower than the density of the particles, the devices for centrally removing these fluids may become very bulky, and may limit the height or length of the reactor. The quantity of fluid that must be injected to transfer the necessary angular momentum to the solid particles is very high and it may prevent the formation of a thick and dense fluidized bed and the proper separation of the fluid and the solid particles.
In fact, when a fluid is injected at high velocity, tangentially to the cylindrical wall and perpendicularly to the axis of symmetry of a cylindrical chamber traversed by a central duct comprising discharge openings for removing this fluid, the fluid can make several turns around this central duct before penetrating thereinto if the discharge openings are narrow. However, as soon as solid particles are introduced into this cylindrical chamber, they slow down the fluid to the extent commensurate with the ratio of the specific gravity of the solid particles to that of the fluid. Accordingly, the removal of the fluid becomes more direct, and this may even cause a reversal of the fluid flow along the central duct, downstream of the discharge openings, and generate turbulence which entrains the solid particles toward the outlet, thereby limiting the possibility of forming a thick and dense fluidized bed inside the cylindrical chamber.
In light of the above, it is clear that the formation of a rotating fluidized bed in a reactor faces various problems. It is the object of the present invention to provide an improved rotating fluidized bed device, and more particularly, a rotating fluidized bed device which at least partially solves the abovementioned problems. In particular, it is the object of the present invention to provide a rotating fluidized bed device in which the injection of one or more fluids is corrected, and in which the formation of the fluidized bed is improved.